The principal objective of the proposed study is to evaluate the effect of L-5-hydroxy tryptophan-pyridoxin administration upon the motor, social, language, and intellectual development of young children with Down's Syndrome. It is designed to test the hypothesis that specific metabolic correction will significantly enhance the overall development of the child with Down's Syndrome. Service to the families of the patients has been incorporated into the design of the study. Infants with Down's syndrome are assigned in random fashion to the placebo or treatment group. During the periodic evaluations - which start at birth and continue through the third birthday - developmental parameters will be assessed by a team including an anthropologist, neurologist, psychologist, physiotherapist, social worker, speech pathologist, and nurse. In addition, laboratory investigations concerning the qualitative and quantitative determination of specific tryptophan derivatives will be pursued. Since the initiation of the Down's syndrome -5-hydroxy tryptophan study we have observed 2 Down's syndrome children in the experiment group developing Infantile spasms. In order to investigate whether there is a definite relationship between the administration of -5- hydroxy tryptophan in children with Down's syndrome and the development of seizures, to find early indicators conceivably leading to Infantile spasms, and to study pathogenetic mechanisms relating to hypsarrhythmia we intend to engage in clinical, laboratory EEG studies. Thus, 36 Down's syndrome children will be admitted during the ensuing study here. They will undergo neurological investigations, EEG's will be performed, and specific Laboratory procedures will be carried out at specified time. (at birth, 3 mos., 6 mos., and 12 mos.).